Chlorofluorocarbons (CFCs) are synthetic chemical compounds widely used in refrigeration and air conditioning; as aerosol propellants and solvents; in forming foams, including those used in fast-food packaging; and in rigid insulation. Scientists now view these synthetic chemicals as the main threat to Earth's protective ozone layer. Because CFCs are immune to destruction in the troposphere, and because they eventually float upwardly, their manufacture and release have lead to the accumulation of large amounts in the stratosphere. In the stratosphere, CFCs are broken down by sunlight into chlorine, which has a catalytic and destructive effect on ozone. The result has been a significant decline in the global ozone shield and an increase in the amount of harmful ultraviolet radiation reaching the surface of Earth. According to a United Nations' study, every 1 percent drop in ozone will lead to a 3 percent increase in non-melanoma skin cancers in light-skinned people, as well as dramatic increases in cataracts, lethal melanoma cancers, and damage to the human immune system. Higher levels of UV light may also worsen ground-level pollution and hurt plants, animals, and especially light sensitive aquatic organisms.
As a result, destruction of CFCs, and in some instances, reclamation of CFC refrigerants is a vital component of the national and global strategies for protection of the earth's ozone layer in a manner consistent with minimal economic disruptions associated with the phase-out of this class of chemicals. There are still sizable reserves of CFCs on hand which must be treated and converted to environmentally benign substances. Likewise, until existing refrigeration and air conditioning equipment is replaced or retrofitted with devices which are capable of operating with more environmentally friendly refrigerants, as CFC production is curtailed and eventually eliminated, industry and consumers must rely increasingly on the availability of reclaimed refrigerants.
Various methods have been proposed for the destruction of unwanted CFCs, such as thermal oxidation, catalytic decomposition, supercritical water oxidation, plasma destruction methods, biological processes, UV photolysis, to name but a few. Many are either in experimental stages of development, economically unattractive or incapable of selectively decomposing only specifically targeted compounds.
One other method for the destruction of CFCs is disclosed in U.S. Pat. No. 5,110,364 by Mazur et al, which provides for chemically degrading unwanted CFCs by dehalogenation reactions through solvated electron chemistry. Mazur et al disclose the formation of solvated electrons through dissolving metal reactions with nitrogen-containing bases, such as ammonia wherein chlorine atoms of the CFC compound are removed during the process to yield products having reduced environmental impact. A somewhat related process is also described in Japanese unexamined application 59-10329 (1984) to Showa Denko KK. Contrary to the disclosures of the earlier Showa Denko process, Mazur et al discovered the reduction of CFCs or other chlorinated organics, e.g. PCBs, with solvated electrons could be successfully carried out in the presence of substances previously thought to interfere with the stability of the solvated electrons or selectivity of the reaction. Mazur et al discovered the need for removing previously considered competing substances, such as oxygen, carbon dioxide, water, etc., from the reaction mixture was not required, and such costly pretreatment step(s) could be omitted.
Such earlier methods for the destruction of CFCs with solvated electrons may be demonstrated by the following representative reaction: EQU Cl.sub.2 F.sub.2 +8Na+4NH.sub.3 .fwdarw.2NaCl+2NaF+CH.sub.4 +4NaNH.sub.2
Sodium amide would then be converted to ammonia and sodium hydroxide as moisture becomes available as shown by the following equation: EQU 4NaNH.sub.2 +4H.sub.2 O.fwdarw.4NaOH+4NH.sub.3
While such reactions with solvated electrons provide a useful and practical solution for disposing of fluorocarbon compounds, including CFCs, in practice metal consumption and solvent requirements, e.g. sodium and ammonia are significant cost elements. Together, the two can make up as much as 70 percent of total operating costs. Of the two main reactants, ammonia is the far less costly, and processes for ammonia recovery are available. However, metals such as calcium, sodium and potassium are non-recoverable, and more costly consumable reactants which can detract from economics of the process.
Application Ser. No. 08/207,289, filed Mar. 7, 1994, now U.S. Pat. No. 5,414,200 by Robert W. Mouk and Albert E. Abel provides for an improved process based on the surprising observation that anhydrous liquid ammonia is a sufficiently strong base that it can react with and totally dehalogenate halofluorohydrocarbon refrigerants, like chlorodifluoromethane (Freon.RTM. 22) according to the following equation: EQU HCClF.sub.2 +5NH.sub.3 .fwdarw.NH.sub.4 Cl+2NH.sub.4 F+NH.sub.4 CN
This reaction coupled with the surprising discovery that apparently complete destruction of halofluorocarbons can be accomplished with solvated electron solutions containing substantially less than stoichiometric amounts of metal led to the discovery that CFC destruction can be achieved by the following pathway: EQU CCl.sub.2 F.sub.2 +2Na+4NH.sub.3 .fwdarw.2NaCl+2NH.sub.4 F+NH.sub.4 CN
Although the Mouk et al process represents a significant advantage over earlier methods in that reactive metal consumption is effectively reduced by a factor of four, the process can nevertheless result in the formation of potentially hazardous ammonium cyanide.
Accordingly, it would be highly desirable to have a more improved process for the dehalogenation and destruction of fluorocarbons, and particularly CFCs, which allows for consumption of significantly reduced levels of metals and other reactants while also eliminating potentially hazardous by-products.